Patent document No. 1 discloses a submersible power generator comprising inner and outer armatures, propellers for rotating the inner and outer armatures relative to each other, and a casing for accommodating the inner and outer armatures, which submersible power generator comprises a power generation mechanism provided with a pair of front and rear outer rotational armatures and a pair of front and rear inner fixed armatures, a pair of front and rear propellers rotating in directions opposite to each other to rotate the pair of front and rear outer rotational armatures in directions opposite to each other, and a casing for accommodating the pair of inner fixed armatures and shielding them from an external environment, wherein the submersible power generator is connected to an anchor installed on a bottom of a water body through a mooring wire, installed under water to operate in a water current, and buoyancy F acting on the submersible power generator is larger than gravity W acting on the submersible power generator during operation of the submersible power generator.
When gravity W acting on the submersible power generator is larger than buoyancy F acting thereon in the Patent document No. 1, the submersible power generator must be moored in water by a mooring wire or a support member extending from a structure on or above a water surface.